in 1971, he worked as an official for the National Union of Tailors and Garment Workers. Corbyn began a course in Trade Union Studies at North London Polytechnic but left after a year without a degree after a series of arguments with his tutors over the curriculum. He worked as a trade union organiser for the National Union of Public Employees and Amalgamated Engineering and Electrical Union where his union was approached by Tony Benn and "encouraged ... to produce a blueprint for workers' control of British Leyland"; the plans did not proceed after Benn was moved to a different Department.

He was appointed a member of a district health authority and in early 1974, at the age of 24, he was elected to Haringey Council in South Hornsey ward. After boundary changes in 1978 he was re-elected in Harringay ward as councillor, remaining so until 1983. As a delegate from Hornsey to the Labour Party conference in 1978, Corbyn successfully moved a motion calling for dentists to be employed by the NHS rather than private contractors. He also spoke in another debate, describing a motion calling for greater support for law and order as "more appropriate to the National Front than to the Labour Party".Corbyn became the local Labour Party's agent and organiser, and had responsibility for the 1979 general election campaign in Hornsey. Around this time, he became involved with London Labour Briefing, where he was a contributor and member of the editorial board during the 1980s. It has been reported that he served as its general secretary for some time. He worked on Tony Benn's unsuccessful deputy leadership campaign in 1981. He was keen to allow former International Marxist Group member Tariq Ali to join the party, despite Labour's National Executive having declared him unacceptable, and declared that "so far as we are concerned ... he's a member of the party and he'll be issued with a card." In May 1982, when Corbyn was chairman of the Constituency Labour Party, Ali was given a party card signed by Corbyn; in November the local party voted by 17 to 14 to insist on his membership "up to and including the point of disbandment of the party".In the July 1982 edition of London Labour Briefing, Corbyn opposed expulsions of the Militant tendency, saying that "If expulsions are in order for Militant, they should apply to us too." In the same year, he was the "provisional convener" of "Defeat the Witch-Hunt Campaign", based at Corbyn's then address.